1. Field of the Invention
The present invention relates to low temperature curable spin-on glass materials which are useful for electronic applications. More particularly, the invention pertains to low temperature curable spin-on glass materials which are useful for optical device fabrication.
2. Description of the Related Art
In the electronic component manufacturing industry, there is a continuing need for spin-on dielectric materials which are curable at low temperatures, i.e. at about 250° C. or less.
The production of display devices such as electrooptic elements, thin film transistors, and display devices is known from U.S. Pat. No. 6,674,106, which is incorporated herein by reference. The fabrication of such components often requires the deposition of light transmissive dielectric materials used as flattening agents and passivation layers, onto features present on substrates in order to achieve proper isolation between devices. Each feature is separated by the insulating layer filled between them. These flattening agents and passivation layers need to fill spaces between narrow features without cracking and creating voids. In the manufacture of optical devices such as flat panel displays, these flattening agents and passivation layers need to have a field breakdown voltage of about 2.5 MV/cm or more and a transparency to light in the range of about 400 nm to about 700 nm of about 95% or more. While such has been attainable with spin-on glass compositions which are cured at relatively high temperatures, layers having these properties has not been heretofore achieved with spin-on glass compositions which are cured at relatively low temperatures, i.e. at a temperature of about 250° C. or less.
Silicon-based dielectric films such as silicate, silazane, silisequioxane or siloxane generally exhibit good gap-fill properties. The silicon-based dielectric films are formed by applying a silicon-containing pre-polymer onto a substrate followed by crosslinking. Historically, silicon-based dielectric films exhibit stability in film thickness, crosslinking density and other enhanced film properties, such as, minimum moisture absorption, high field breakdown voltage, low current leakage and resistance to organic solvent/chemicals after high temperature cures which exceed 400° C. In optical applications, organic materials that are being used as a part of the device are often unstable at temperature higher than 275° C. Thus, there exists a need in the art for dielectric spin-on materials that provide crack-free and void-free gap-fill of narrow features at low process temperatures. Such materials should also have adequate mechanical strength to withstand chemical mechanical polishing and have enhanced wet etch resistance. Films can be achieved at low temperatures by using a condensation/cross-linking catalyst including ammonium compounds, amines, phosphonium compounds and phosphine compounds. Through the use of a catalyst one can effectively lower the condensation temperature and/or drive the extent of crosslinking of silanol groups. A balance between the amount of organic content, density of the film and mechanical strength has to be maintained. Silicon-based dielectric films having a field break down values (FBD), ranging from about 2.5 MV/cm or above, can be produced by the methods of the invention. Typically, silicon-based dielectric films, including silica dielectric films, are prepared from a composition comprising a suitable silicon containing pre-polymer and a catalyst, such as a metal-ion-free catalyst and one or more optional solvents and/or other components may also be included. The dielectric precursor composition is applied to a substrate suitable, e.g., for production of a semiconductor device, such as an integrated circuit (“IC”) or optics, by any art-known method to form a film. The composition is then crosslinked, such as by heating to produce a gelled film. The gelled film is then heated at a temperature of 250° C. or less to produce a stable film.
The films produced by the processes of the invention have a number of advantages over those previously known to the art, including improved field break down strength, that enables the produced film to be used in the optics. The property of a stable dielectric constant is advantageously achieved without the need for further surface modification steps to render the film surface hydrophobic, as was formerly required by a number of processes for forming silica dielectric films. Instead, silicon-based dielectric films as produced by the processes of the invention are sufficiently hydrophobic as initially formed.